This invention relates to weighbelt apparatus.
In process control, where accurate flow of material is required, weighing units are used to measure the mass of material transported. Flow control is obtained by either varying the flow speed of the material or the thickness of the layer of material transported over the weighing device. For effective control the weighing device must measure the mass of the material with a considerable degree of accuracy.
In U.S. Pat. No. 4,509,609 a weighbelt apparatus which gives very accurate results has already been proposed. This apparatus has a belt upon which material is moved across the apparatus, a generally planar support for the belt extending across the apparatus, belt lifting means connected to the apparatus and arranged to lift the belt out of contact with the planar support during operation of the apparatus, and means arranged to apply a known downward force to the planar support in order to calibrate the apparatus. The calibration procedure is fully described in the U.S. patent.
In this apparatus it has been found that spurious effects can arise due to uneven loading or uneven lateral distribution of the load on the belt over the planar support.